Debian

Debian is a widespread Linux release, that's used primarily on desktop machines, still many people have begun using it lately as a web server OS as well, due to the stability and protection it offers. The latter is a consequence of the fact that Debian is developed and supported by thousands of qualified volunteers all around the world, so that any patch that's needed to fix a certain issue is released in a few days. The very same community can also help you with any question or trouble that a user may ever encounter, as they can be contacted via e-mail using e-mail lists and a competent response will be sent in around 15-20 min. The advantage here is that your questions will be replied by the same people who have created the Operating System itself and they have a detailed knowledge of how it functions. As Debian is provided for free, you won't need to pay any license fees to use it and you'll be able to personalize it as much as you want or need. This is valid for both the Operating System as well as the 30.000+ software packages which are available for it.